This invention relates generally to turbines which use steam or other vapors or gases at high pressures and temperatures as the working fluid. More particularly it relates to a manually positionable safety trip valve with automatic closing from any position when called for by adverse operating conditions and means generally manual to control opening movement when the adverse operating condition is corrected.
A trip valve system of the type to which this invention pertains was described in my prior U.S. Pat. No. 3,556,463. A further improvement to control the velocity of the trip valve elements when it is automatically moved to closed position to prevent excessive impact forces during such closing movement is disclosed in my co-pending application, Ser. No. 564,698, filed Apr. 3, 1975.
A feature of the invention covered by my U.S. Pat. No. 3,556,463 was the incorporation of snubbing or cushioning chambers to slow the moving parts of the trip valve as they are moved from the closed to open position on automatic response to correction of the adverse operating condition.
Experience with trip valves made in accordance with my prior patent has shown that the last mentioned objective was attained for valves in a range up to 3 inches. However, with larger sized valves the physical size of the turbines and the driven equipment increases exponentially. The larger inertia of the rotors of the turbine and the driven equipment thereon at all times requires slow controlled starting by the operator to avoid physical damage to the rotary components of the turbine due to abrupt opening action of the trip valve when the adverse operating condition for tripping the valve to closed position is corrected. The present invention acts to prevent the trip valve from leaving the closed position until an external control has been applied to the moving elements of the trip valve, and then to permit opening only as the external control dictates. As in the prior art device, automatic tripping to the closed position will occur from any operating position of the trip valve whenever called for by an adverse operating condition of the associated turbine or like device. However, the trip valve will not leave the closed position until the external positioning means is used to control opening of the trip valve.
This arrangement also provides a collateral advantage in that the operator can control the opening rate of the trip valve from the closed position without shutting off or throttling the steam supply upstream of the trip valve, and thus prevent any adverse operating conditions from occurring in the associated turbine when steam or other operating fluid is readmitted to place the turbine back into operation.